Jung Han. Innovations in Food Packaging

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Antimicrobial

packaging systems

JungH.

Han

Introduction 80

Food safety 81

Antimicrobial packaging 82

Antimicrobial agents 83

System design 86

Commercialization 94

References 101

Introductmn

The quality of foods has been defined as their degree of excellence, and includes fac-

tors of

taste,

appearance and nutritional content. Quality is the composite of charac-

teristics that have significance and make for acceptability. However, acceptability can

be highly subjective. Based on deterioration factors and determination procedures,

quality may include various aspects such as sensory quality, microbial quality, and

toxicological quality. These aspects are not separated from one another- for example,

microbial contamination damages sensory quality and safety. Microbial food quality

relates to all three groups of factors, since the growth of bacteria generates undesir-

able odors and life-threatening

toxins,

changes the color, taste and texture of food, and

also reduces the shelf life of the product. Microbial growth on packaged foods

signif-

icantly decreases the safety of food and the security of

public

health. In our society,

fast foods, convenience foods and fresh foods are essential elements. Many food

industries produce minimally processed foods, precut

fi*uits/vegetables,

and ready-to-

eat foods for the purpose of maximized convenience and

fi*eshness.

In these environ-

ments of food manufacturing on a mass-production scale, food safety is a top priority

and issue

for producers, the food

industry,

governments, and public

consumers.

Improper

treatment and accidental cross-contamination of foods can cause major problems of

recall and serious food-borne illness. Furthermore, the safety of food and related

pub-

lic health issues can be jeopardized

malicious tampering, extortion for benefits, tri-

als to obtain

public

attentions for any

reasons,

and terrorism (Kelly et a/., 2003). Since

ISBN:

0-12-311632-5

All rights of reproduction in any form reserved

Antimicrobial packaging systems 81

the

2001

tragedy of the World

Trade

Center

the

consideration of food and water safety

has assumed major importance, and the security of food chains against bioterrorism

regarded

a significant aspect of pubhc safety

(Nestle,

2003).

Food safety

has

become

a significant subject of trends in food

packaging,

logistics, trade, and consumer studies.

Food safety

Spoilage of food products

Most foods

are

perishable.

Spoilage of foods is caused both biologically and chemically.

In addition

to the

chemical degradation of food ingredients through oxidation processes,

most spoilage processes are due to biological reasons such as auto-degradation of

tis-

sues by enzymes, viral contamination, protozoa and parasite contamination, microbial

contamination, and loss by rodents and

insects.

The growth of micro-organisms is the

major problem of food spoilage leading to degraded quality, shortened shelf

life,

and

changes

natural microflora that could induce pathogenic

problems.

Microbial spoilage

of food products is caused by many bacteria, yeast and molds; however, their sensi-

tivities to the spoilage are dependent on nutrients, pH, water activity, and presence of

oxygen. Therefore, the many different potential micro-organisms that could contami-

nate food products and the various growth environments present difficult problems in

preventing the spoilage.

For the food industries, the prevention of food spoilage is a very important issue in

determining profit. Furthermore, reducing food spoilage can prolong the shelf life of

food products and accordingly extend market boundary, resulting in increased profit.

Food-borne illness

Food-borne ilhiess is caused by contamination of food products by micro-organisms or

microbial

toxins.

Many food-processing technologies

have

been developed

prevent the

contamination and inactivation of

pathogens.

Traditionally, thermal processes such as

blanching, pasteurization, and commercial sterilization

have

been used for

the

elimination

of pathogens from food products. Currently, various new non-thermal technologies are

being studied to assess their effectiveness and

mechanisms.

Such new processes include

irradiation, pulsed electric

fields,

high-pressure processes, and the use of new antimicro-

bial agents. However, these new technologies cannot completely prevent the contam-

ination and/or growth of

pathogens.

Some of these methods still require regulatory

permission for their commercial

use.

It is also very hard

control pathogens because of

the wide variety of microbial physiology, pathogenic mechanisms, and passage of con-

tamination; the complexity of food composition; their sensitivity

antimicrobial agents;

the mass-production nature of food

processing;

and difficulties in early detection.

There are many prevention systems that are used by the food industry, such as haz-

ard analysis and critical control points (HACCP), sanitation standard operating pro-

cedures (SSOP), good manufacturing practice (GMP), and various inspections. The

82 Innovations in Food Packaging

good practice of these quality systems is much

important and effective in ehminat-

ing pathogen problems from food system than is the use of reliable new technologies.

Malicious tampering and bioterrorism

One of primary functions of food packaging is to protect food from unintentional con-

tamination and undesirable chemical reactions, as well as providing physical protec-

tion. However, recently, the need

has

arisen for packaging systems to be capable of the

protection of the food from intentional contamination - i.e. malicious tampering

(Kelly et

al.,

2003).

To secure food safety from tampering and bioterrorism, many sys-

tematic protocols are required - such as new food and drug regulation, and new secu-

rity acts (e.g., Bioterrorism Acts and Homeland Security guideline for imported goods).

Enhanced traceability is also required so that any potentially tampered goods can be

removed

from

the food

chain.

Security against tampering and terrorism can be improved

by systematic preparation, practical regulation, inspection, emergency response train-

ing, and other systematic protocols. However, issues such as traceability, food secu-

rity, and safety enhancement involve technical development, such as a database for

tracking products, intelligent packaging for monitoring foreign matters in products,

robotic automation for warehousing, and new security seals on distribution packages.

The protective function of food packaging has become more significant with respect

to safety enhancement. Among all of the potential technologies, practical approaches to

enhance the safety of food products include the use of advanced tamper-evident or

tamper-resistant packaging, and intelligent packaging that indicates any tampering and

contamination and has a high-barrier design (Rodrigues and Han, 2003). The use of

tamper-evident packaging and intelligent packaging is highly desirable to minimize the

risk of

the

malicious activities of

terrorists

endangering public safety through the food

product chain, hi addition

the visual indication of disintegration and contamination of

packages, antimicrobial packaging systems can kill or inhibit the growth of pathogenic

micro-organisms that may be injected into packaged foods without any visual evidence

tampering.

With

the positive

contribution to food safety of

the new

smart design of food

packaging, antimicrobial packaging systems can

also

protect food products more actively.

Tamper-evident packaging and intelligent packaging are considered to be passive

monitoring

systems.

Antimicrobial packaging can reduce the risk of tampering and

bio-

terrorism by eliminating contaminating micro-organisms as well as maintaining the

quality of packaged food products by reducing the potential for cross-contamination

of food products with spoilage and pathogenic micro-organisms.

Antimicrobial packaging

system that can kill or

inhibit the growth of micro-organisms

and thus extend the shelf life of perishable products and enhance the safety of packaged

products (Han,

2000).

Antimicrobial packaging

can kill or

inhibit target micro-organisms

(Han, 2000, 2003a). Among many applications such as oxygen-scavenging packaging

Antimicrobial packaging systems 83

and moisture-control packaging, antimicrobial packaging is one of the most promising

innovations of active packaging technologies (Floros

al, 1997). It can be constructed

by using antimicrobial packaging materials and/or antimicrobial agents inside the

package space or inside foods. Most food packaging systems consist of the food prod-

ucts,

the headspace atmosphere and the packaging materials. Any one of these three

components of food packaging systems could possess an antimicrobial element to

increase antimicrobial efficiency.

Antimicrobial packaging research generally started with

the

development of antimi-

crobial packaging materials that contain antimicrobial chemicals in their macromole-

cular structures. However, without the use of alternative packaging

materials,

common

packaging materials can be utilized for antimicrobial packaging systems when there

is antimicrobial activity in packaged foods or in the in-package atmosphere. Edible

antimicrobial agents can be incorporated into food ingredients, while antimicrobial

resources can

interleaved in

the

in-package headspace in the form of sachets, films,

sheets or any in-package supplements, to generate antimicrobial atmospheres.

Besides the use of antimicrobial packaging materials or antimicrobial inserts in the

package headspace, gaseous agents have been used to inhibit the growth of micro-

organisms. Common gases are carbon dioxide for modified atmosphere packaging,

sulfur dioxide for

berries,

and ethanol vapor for confections. These gases are injected

into the package headspace or into palletized cases after shrink-wrapping of a unit

load on

pallet.

Vacuum, nitrogen-flushing and oxygen-scavenging packaging, which

were originally designed for preventing the oxidation of packaged foods, also possess

antifungal and antimicrobial properties against aerobic bacteria as a secondary func-

tion, since these micro-organisms are restrictively aerobic (Smith et al., 1990; Han,

2003b). However, these technologies, which control the low oxygen concentration to

inhibit the growth of aerobic micro-organisms, could cause the onset of anaerobic

microbial growth. Controlling anaerobic bacteria in modified atmosphere packaging

is a very important issue in maintaining the quality and safety of the products.

Antimicrobial agents

Various antimicrobial agents could be incorporated into conventional food packaging

systems and materials to create new antimicrobial packaging systems. Table 6.1 shows

potential antimicrobial agents and food-grade preservatives. They can generally be

classified into three groups; chemical agents, natural agents, and probiotics.

Chemical antimicrobial agents

For the purpose of food preservation, all packaging ingredients should be food-grade

additives. The chemical agents can be mixed with food ingredients, incorporated into

packaging additives or inserted into the headspace atmosphere. The antimicrobial

agents are in contact with and consumed with the food products in these applications.

> i Innovations in Food Packa

ging

Classification

Organic acids

Acid salts

Acid anhydrides

Para benzoic acids

Alcohol

Bacteriocins

Fatty acids

Fatty acid esters

Chelating agents

Enzymes

Metals

Antioxidants

Antibiotic

Fungicides

Sanitizing gas

Sanitizers

Polysaccharide

Phenolics

Plant volatiles

Plant/spice extracts

Probiotics

Antimicrobial agents

l^^iriaiificKr!^^

packaging systems

Acetic

acid,

benzoic

acid,

lactic

acid,

citric

acid,

malic

acid,

propionic

acid,

sorbic

acid,

succinic

acid,

tartaric

acid,

mixture of organic acids

Potassium sorbate, sodium benzoate

Sorbic anhydride, benzoic anhydride

Propyl paraben, methyl paraben, ethyl paraben

Ethanol

Nisin,

pediocin, subtilin, lacticin

Laurie

acid,

palmitoleic acid

Glycerol mono-laurate

EDTA, citrate, lactoferrin

Lysozyme, glucose oxidase, lactoperoxidase

Silver,

copper, zirconium

BHA,BHT,TBHQ, iron salts

Natamycin

Benomyl,

Imazalil, sulfur dioxide

Ozone, chlorine dioxide, carbon monoxide, carbon dioxide

Cetyl pyridinium chloride, acidified NaCi, triclosan

Chitosan

Catechin,

cresol, hydroquinone

Allyl isothiocyanate, cinnamaldehyde, eugenol, linalool, terpineol, thymol,

carvacrol,

pinene

Grape seed extract, grapefruit seed extract, hop beta

acid,

Brassica erucic acid

oil,

rosemary oil, oregano oil, basil oil, other herb/spice extracts and their oils

Lactic acid bacteria

Modified from Han (2000, 2003a, 2003b); Suppakul

etal.

(2003a).

Therefore, the chemical antimicrobial agents should

controlled as food ingredients

regardless of where the chemical antimicrobial agents were positioned initially - in

the food products, in the packaging materials, or in the package headspace atmos-

phere. In the case of non-food-grade chemicals, the only way to incorporate the chem-

ical into the food packaging system

through

the

chemical binding of the antimicrobial

agents to packaging material polymers (immobilization). In this case, the migration or

residual amount of the non-food-grade chemical in the food products is prohibited by

regulation. Therefore, it is necessary to verify that there is no migration of the chem-

ical

from

packaging materials to foods, and there is no residual free chemical after the

immobilization reaction. There will be detailed explanation of the immobilization

system later in this chapter.

The most common chemical antimicrobials used by researchers are the various

organic acids. Organic acids are widely used as chemical antimicrobial agents because

their efficacy is generally well understood and cost effective. Many organic acids,

including fatty acids, are naturally existing chemicals and have been used historically.

Currently, most of them are produced by chemical synthesis or chemically modified

from natural acids. Organic acids have characteristic sensitivities to micro-organisms.

For example, sorbic acid and sorbates are very strong antifiingal agents, while their

antibacterial activities are not effective - they have various antimicrobial mecha-

nisms. Therefore, the correct selection of organic acids is essential to have effective

Antimicrobial packaging systems 85

antimicrobial agents. Mixtures of organic acids have a wider antimicrobial spectrum

and stronger activity than a single organic acid.

Fungicides are also common antimicrobial agents. Imazalil has been incorporated

into the wax coating of oranges and other citrus fruits. Since fungicides are not per-

mitted as a direct food preservative, they cannot be mixed into food ingredients or

added

food-contact packaging materials as food-contact substances. Therefore, it is

necessary

design antimicrobial food packaging systems when non-food-grade antimi-

crobial

agents,

such

fungicides,

are

used.

Food sanitizers and another chemical antimi-

crobial groups are included in

Table

6.1.

They are food cleansing agents, food contact

substances or food contact surface sanitizers. Residual food sanitizers on foods are

permitted, with specific control

limits.

Thus the use of food sanitizers has many advan-

tages over the use of other non-food-grade antimicrobial agents such as fungicides.

Natural antimicrobial agents

Table

6.1

includes herb

extracts,

spices, enzymes, and bacteriocins

naturally occurring

antimicrobial agents. Looking to the consumers' demand for chemical preservative-

free foods, food manufacturers are now using naturally occurring antimicrobials to

sterilize and/or extend the shelf life of

foods.

Herb and spice extracts contain multiple

natural compounds, and are known to have a wide antimicrobial spectrum against var-

ious micro-organisms. Apart from antimicrobial activity, other advantages they offer

include antioxidative activity and their effect as alternative medicines. However, their

mode of action and kinetics are generally

unknown,

and their chemical stability

also

concern.

In addition, they create some problems with respect to flavors.

Specificity of

enzymes

should be considered carefully, since antimicrobial activity

is very sensitive to the environments and substrates. For an example, the activity of

lysozyme can

significantly affected by temperature and

pH.

In most

cases,

lysozyme

is not effective against gram-negative bacteria. This is due to the complex cell wall

structure of gram-negative bacteria and the specificity of lysozyme for peptidoglycan.

Various bacteriocins, such as nisin, pediocin, lacticin, propionicin etc., can be incor-

porated into foods and/or food packaging systems to inhibit the growth of spoilage and

pathogenic micro-organisms (Daeschul, 1989). The extracted bacteriocins, which are

generally small molecular weight

peptides,

can be utilized in various

ways;

however, it

very important

characterize their resistance to thermal treatment and

pH.

In the

case

of fermented food products,

live

bacteria which produce bacteriocins can be intentionally

added

probiotics in the packaged food system

obtain antimicrobial effectiveness.

Probiotics

Table 6.1 also shows the possible use of probiotics

{Lactobacillus reuteri)

to control E.

coli

0157:H7 (Muthukumarasamy

etal,

2003).

Various

micro-organisms,

e.g.

lactic acid

bacteria, produce bacteriocins and non-peptide growth-inhibiting chemicals such as

reuterin. These naturally produced antimicrobials can inhibit the growth of other bac-

teria. Use of probiotics can therefore effectively control the competitive undesirable

86 Innovations in Food Packaging

micro-organisms. Many traditional fermented food products contain antimicrobial

probiotics. There has been much research and development regarding the function of

antimicrobial probiotics for the preservation of fermented foods. Currently there is

only limited research into the use of probiotics for the purpose of antimicrobial pack-

aging design. With the new technology development for the delivery of live probi-

otics,

the use of probiotics as an antimicrobial source for antimicrobial food packaging

will be more popular in future due to its safety and effectiveness.

System design

There are various factors to be considered in designing antimicrobial systems.

Antimicrobial systems can be constructed by using antimicrobial packaging materi-

als,

antimicrobial inserts (such as sachets) to generate antimicrobial atmosphere con-

ditions inside packages, or antimicrobial edible food ingredients in the formulation of

foods.

Since antimicrobial packaging systems are designed to control the growth of

micro-organisms in packaged foods, the systems essentially consist of packaging mate-

rials (or packages), foods, the in-package atmosphere, target micro-organisms, and

antimicrobial agents. These five elements are related to one another and to the final

system design features.

To study the effectiveness of antimicrobial food packaging systems with respect to

the relative effects of these elements, many choices of combinations should be exam-

ined using real food

systems.

The majority of research

has

been conducted using culture

media, which provides the

richest

nutritional quality and

the

most favorable environment

for microbial growth, and antimicrobial packaging materials. Most micro-organisms

in culture media are not stressed compared to micro-organisms under normal condi-

tions in foods. Many antimicrobial systems that

have

shown strong antimicrobial activity

against target micro-organisms in culture media do not demonstrate the same antimi-

crobial activity when they are actually in the food systems. This is very common, and

clearly shows the interactive effects of food ingredients, micro-organisms, and antimi-

crobial agents. All of these factors have complex systems that cannot be explained by

a single chemical mechanism. Therefore, it

strongly recommended that experiments

regarding the efficiency examination of an antimicrobial packaging system should be

conducted using a real food instead of culture broth or agar media. Table 6.2 lists

examples of antimicrobial food packaging systems which have been tried, mostly by

university researchers, over the past two decades.

Antimicrobial mechanisms

An antimicrobial agent has specific inhibitory activity and mechanisms against each

micro-organism. Therefore, the selection of antimicrobial agents is dependent on their

efficacy against a target micro-organism. There is no "magic bullet" antimicrobial

agent that will work effectively against all spoilage and pathogenic micro-organisms,

because all antimicrobial agents have different activities which affect micro-organisms

Antimicrobial packaging systems 87

Table 6.2 Antimicrobial food packaging systems constructed by researchers

Antimicrobial agents Packaging materials

Organic acids

Benzoic acids

Foods

Para-benzoate

Benzoic and sorbic

acids

Sorbates

Sorbate and

propionates

Acetic, propionic acid

Enzymes

Lysozyme

Lysozyme, nisin, EDTA

Lysozyme, nisin,

propyl paraben, EDTA

Immobilized lysozyme

Glucose oxidase

Bacteriocins

Nisin

lonomer

LDPE

PE coating

Styrene-acrylate

PE-co-Met-acrylate

LDPE

OE,

BOPP, PET

LDPE

MC/palmitic acid

MC/HPMC/fattyacid

MC/chitosan

Starch/glycerol

WPI

CMC/paper

PE/foil

Chitosan

PVOH

SPI,zein

WPI

Tilapia fillets

Culture media

Simulants

Culture media

Water,

cheese

Cheese

Water

Culture media

Chicken breast

Culture media

Cheese

Culture media

Apples

Water

Culture media

Nisin,

lacticins

PVOH,

nylon,

cellulose acetate

HPMC

H PMC/stearic acid

Corn zein

Corn

zein,

wheat gluten

Ethylene-co-acrylic

LDPE,

poly-amide

LDPE,

poly-amide

Culture media

Fish

Beef

Culture media

Shredded cheese

Culture media

Oyster, beef

Micro-organisms

Total bacteria

Pen.

spp.,

Asp.

niger

Migration test

cerevisiae

Asp.

niger,

Penn.

spp.

cerevisiae

Migration test

Yeast, mold

Migration test

cerevisiae,

Asp.

niger,

Penn.

rogueforti

cerevisiae,

molds

Firmness test

Migration test

coli,

Lactobacillus

plantarum

Lis.

monocytogenes,

Sal.

typhimurium,

coli

0157:

H7,

thermosphacta,

aureus

Lysozyme activity test

thermosphacta

Lis.

monocytogenes,

Staphyl.

aureus

Lis.

monocytogenes,

aureus

Total aerobes

Lactobacillus plantarum

Lactobacillus leichmannii

M. flavus.

Lis.

monocytogenes

Total aerobes, coli-form

Researchers

Huang et^/., 1997

Weng etaL, 1997

Dobiaset^/., 2000

Chung

et£?/.,

2001a

Chung ett?/., 2001b

Weng

etal.,

1999

Han and Floros, 1997

Han and Floros,

1998a, 1998b

Devlieghere

etal.,

2000a

Rico-Pena and Torres,

1997

Vojdani and Torres,

1990

Chen etaL, 1996

Baron and Sumner,

1993

Ozdermir, 1999

Ghoshet< 1973,1977

Weng and Chen, 1997;

Weng and Hotchkiss,

1993

Yakovlevaet^/., 1999

Outtaraet^/., 2000a

Buonocore

etal.,

2003

Padgett et^/., 1998

Rodrigues and Han,

2000;

Rodrigues

etal.,

2000

Appendini and

Hotchkiss, 1996, 1997

f'\e\ds

etal.

1986

Siragusaet^/., 1999

Comsietal.,

2001

Sebtiet^/., 2002

Cookseyettf/.,2000

Dawson

etal.,

2003

Leung

etal.,

2003

etal.,

2000

Kim

etal.,

2002

(Continued)

88 Innovations in Food Packaging

Table 6.2 (Continued)

Antimicrobial agents

Nisin,

EDTA

Nisin,

citrate, EDTA

Nisin,

organic acids

mixture

Nisin,

lauric acid

Nisin,

pediocin

Pediocin

Polymers

Chitosan

Chitosan,

herb extracts

Chitosan acetate

UV irradiation,

excimer laser

Natural extracts

Grapefruit seed extract

Grapefruit seed extract.

lysozyme, nisin

Clove extract

Herb extract.

Packaging materials

PE,

PE-PE oxide

PVC,

nylon, LLDPE

Acrylics, PVA-co-PE

Zein

Soy protein

Cellulose casing

WPI

Chitosan/paper

LDPE

Nylon

LDPE,

nylon

LDPE

Na-alginate,

k-carrageenan

LDPE

Foods

Beef

Chicken

Water

Simulants

Turkey bologna

Turkey breast, ham, beef

Culture media

Cheese

Strawberry

Culture media

Ground beef

Lettuce, soy-sprouts

Culture media

Lettuce, cucumber

Micro-organisms

thermosphacta

Sal. typhimurium

Migration test

Lis.

monocytogenes

Lis.

monocytogenes

Lis.

innocua

Lis.

monocytogenes,

Lis.

innocua

coli

Lb.

plantarum,

coli,

cerevisiae,

Fusarium

oxysporum

coli,

Vibrio

vulnificus,

Sal. typhimirium, Sal.

enteritidis;

Shigella sonnei

Pseudomonas

fluorescens.

Enterococcus

faecalis,

aureus

Total aerobes,

coli-form bacteria

coli,

aureus

L. plantarum,

oxysporum,

coli,

cerevisiae

coli,

aureus.

Leu.

Researchers

Cutter

etal.,

2001

Tatrajan and Sheldon,

2000

Choi et^/., 2001

Hoffman et^/., 2001

Dawson

etal.,

2002

M'mgetal.,

1997

Quintero-Salazar et al.

2003

Coma

ettf/.,

2002

Yi etc?/., 1998

Hong

etc?/.,

2000

Parketal.,

2003

Pa\k

etal.,

1998; Paik

and Kelly, 1995

Haettf/.,

2001

Leeetal.,

1998

Chaettf/.,

2002

\-\ongetal.,2000

etal.,

1998

Ag-zirconium

Cinnam-aldehyde,

eugenol,

organic acid

Horseradish oil

Horseradish extract

and

Lactobac.

reuteri

(probiotics)

Allyl isothiocyanate

Green tea extract

(catechins)

Basil extract

Others

Benomyl

Imazalil

LDPE

Chitosan

Paper in pouch

PE/EVOH/PET pouch

PE film/pad

PVA/starch

LDPE

lonomer

LDPE

Strawberry

Bologna, ham

Ground beef

Chicken,

meats,

smoked salmon

Culture media

Bell pepper

mesenteroides,

cerevisiae.

Asp.

niger.

Asp.

oryzae.

Pen.

chrysogenum

Firmness test

Enterobac, Lactic acid

bacteria. Lb.

sakei,

Serratia.

spp.

£ CO//0157:H7

£co//0157:H7

coli,

enteritidis.

Lis.

monocytogenes

£ coli

Chung

etal.,

1998

Outtara.

etal.,

2000a,

2000b

Nadarajahettf/.,

2002,

2003

Muthukumarasamy

etal.,

2003

Takeuchi and Yuan,

2002

Chen

etal.,

2003

Suppakul

etal.,

2003b

HalekandGarg, 1989

Miller et^/., 1984

Antimicrobial packaging systems 89

liable 6.2

(Continueti^

Antimicrobial agents

Ageless

BHT

Ethanol

Hinokithiol

Chlorine dioxide

Hexanal,

hexenal,

hexyl acetate

Carbon monoxide

Triclosan

Hexamethylenetetramine

Silver zeolite, silver

nitrate

Antibiotics

Packaging materials

LDPE

Sachet

HOPE

Silicagel sachet

Silicon oxide

Cyclodextrin

Plastic films

;sachet

sachet

Modified atmosphere

packaging

Modified atmosphere

packaging

Styrene-co-acetate

LDPE

Foods

Cheese

Bread

Breakfast cereal

Culture media

Bakery

Sliced apple

Pork chops

Culture media

Chicken breast

Orange juice

Culture media

Micro-organisms

Molds

Migration test

coli,

Sal.

entehtidis,

Lis.

monocytogenes

Total bacteria, lactic

acid bacteria

Enterococcus faecalis

Lis.

monocytogenes,

aureus,

Sal enteritidis,

coliO^ 57:H7

Yeast, laaic acid

bacteria

cerevisiae,

coli,

aureus,

Sal.

typhimurium.

Vibrio parahaemolyticus

Sal.

typhimurium,

Klebsiella

pheumoniae,

coli,

aureus

Researchers

Weng and Hotchkiss,

1992

Smith

etal.,

1989

HoojjdLtt

etal.,

1987

Shdipero

etal.,

1978

Smith

etal.,

1987

Gontard,

1997

Ozen and Floros, 2001

Lanciottiet^/., 2003

Krause

etal.,

2003

Chung et^/., 2003

Vermeiren

etal.,

2002

Devlieghereet<^/.,

2000b

Ishitani,

1995

Han and Moon, 2002

MC,

methyl cellulose; HPMC, hydroxypropyl methyl cellulose; WPI, whey protein isolate; CMC, carboxyl methyl cellulose; SPI, soy

protein isolate; PE, polyethylene; PVA, polyvinyl acetate; EVOH, ethylene vinyl alcohol; PVOH, polyvinyl alcohol.

differently. This is due to the characteristic antimicrobial mechanisms and the differ-

ences

physiology of the micro-organisms. Simple categorization of micro-organisms

may be very helpful to select specific antimicrobial agents, which may be categorized

by oxygen requirement (aerobes or anaerobes), cell-wall composition (gram-positive

and gram-negative), growth-stage (spores or vegetative cells), optimal growth tem-

perature (thermophilic, mesophilic

psychrotrophic),

or acid/osmosis

resistance.

Besides

the microbial characteristics, the antimicrobial characteristics of the agent are also

important in understanding the efficacy as well as the limits of the activity. For exam-

ple,

some antimicrobial agents inhibit essential metabolic (or reproductive genetic)

pathways of micro-organisms, while others alter cell membrane/wall structure. Two

major fiinctions of microbial inhibition are microbiocidal and microbiostatic effects.

Microbiocidal

It is expected that antimicrobial packaging systems would kill target spoilage and

pathogenic bacteria, since the system could eliminate any micro-organisms from the

food/packaging

system.

Though it

practically

very

hard

to remove all

micro-organisms,

microbiocidal antimicrobial system may kill the target micro-organisms when the

antimicrobial concentration goes above the m.i.c. for a

while.

With other treatment to